This invention relates to a process and apparatus for forming glass filaments by utilization of centrifugal force.
A conventional process and apparatus for forming glass filaments by utilization of the centrifugal force will be described with reference to FIG. 5.
More specifically, molten glass B is continuously supplied from a nozzle K of a forehearth J of a glass melting furnace I to a hollow cylindrical rotary member A rotated at high speed by a drive device H. The molten glass supplied to the member A is discharged in small conical shapes from narrow holes D in a peripheral wall C of the rotary member A under the influence of a centrifugal force. Primary filaments formed on distal end portions of the conical shaped molten glass are fed into a stream G of flame injected from a flame port F of a fiberizing burner E, so that the primary filaments are attenuated into secondary filaments.
In order to form glass filaments being small in diameter and having high thermal insulative properties with this conventional method, various means have be proposed in the art.
A first means is to increase the flow velocity of the flame stream G, assuming that glass of the same kind is used. However, since, with this means, the amount of combustion of the fiberizing burner E must be increased, the temperature of the flame at the flame port F excessively increases and the proportion of formation of the primary filaments into non-fibrous materials of a spherical shape or a hooked shape is increased, thus adversely affecting the flocculent properties.
To avoid this phenomenon, there has been adopted means for increasing the amount of the air for the combustion, as described in U.S. Pat. No. 3,785,791; however, when the air-fuel ratio exceeds a certain value, the combustion becomes unstable, and the production of unburned fuel, an oscillating combustion and etc., are encountered, so that the flame temperature becomes quite uneven, which results in a drawback that the secondary filaments of a uniform diameter can not be obtained.
A second means is to reduce the diameter of the narrow holes D in the peripheral wall C to reduce the diameter of the primary filaments, thereby reducing the diameter of the secondary filaments to be obtained. However, when the diameter of the narrow holes D is reduced, the molten glass can not flow out easily, and therefore the following means need to be added: (a) means for decreasing the amount of supply of the molten glass; (b) means for increasing the number of rotations of the rotary member A; (c) means for increasing the temperature of the molten glass in the rotary member A to lower the viscosity thereof. The means (a) decreases the amount of production of the products, and the means (b) and (c) greatly shorten the lifetime of the rotary member A. Thus, these means are all undesirable.
As a third means, it can be considered to reduce the amount of flow of the molten glass from each narrow hole D (which is formed in the peripheral wall C of the rotary member A) per unit time (the amount of flow of the molten glass from each narrow hole is sometimes referred to as one transition cone amount); however, this reduces the amount of production of the secondary filaments to be obtained. To avoid this reduction of the production, it can be considered to increase the height of the peripheral wall C and to increase the number of the narrow holes D; however, if the height of the peripheral wall C is increased, the lower end portion of the peripheral wall C is remote from the flame port F of the fiberizing burner, and the secondary attenuating by the flame stream G becomes insufficient, so that it is difficult to form the secondary filaments in the vicinity of the lower end portion. Therefore, the height of the peripheral wall C is limited.
If one transition cone amount described above is reduced, the primary filaments become sensitive to the temperature of the flame stream G, and if the temperature is high, the primary filaments are liable to become non-fibrous materials of a spherical shape or a hooked shape, and the secondary filaments become liable to stick to each other, and the flocculent properties are lowered. Therefore, the flame stream temperature lower than usual is needed; however, as described above, the lowering of the flame temperature is limited, and if one transition cone amount is reduced, this must be dealt with by reducing the amount of combustion of the fuel of the fiberizing burner E so as to reduce the thermal energy, so that the distance of reach of the flame stream G becomes shorter. As a result, the height of the peripheral wall C is limited also from this aspect, which incurs a problem of a considerable production reduction.
There are many kinds of glass filaments, and glass filaments of many different diameters, ranging from a small to a large diameter, are required to be produced. However, with the conventional methods and apparatuses, to fiberize many kinds of glass filaments using a common apparatus is not desirable, since this incurs the production reduction, the increase of the thermal energy, a degraded quality of the products, and so on.
Naturally, it is not desirable to provide production lines for exclusive use for forming glass filaments of different kinds, respectively, since this increases the production cost.